In recent years, an X-ray mass estimation apparatus is used in which a measurement target object is irradiated with X-rays and the mass of the measurement target object is estimated (calculated) based on the amount of transmitted X-rays.
With this X-ray mass estimation apparatus, an X-ray transmission image of the measurement target object is obtained, and then, by utilizing a characteristic that the image appears darker when the thickness of a material in the X-ray transmission image is larger, the mass of the measurement target object is estimated according to the brightness per unit area included in the X-ray transmission image, for example, when the brightness is low, the mass is large, and when the brightness is high, the mass is small.
For example, Japanese Laid-Open Patent Application Publication Nos. 2002-520593 (published on Jul. 9, 2002) and 2002-296022 (published on Oct. 9, 2002) disclose an irradiation monitor for material properties and an X-ray mass estimation apparatus, which, in order to calculate the percentage of a fat content in the meat products, detect the amount of transmitted X-rays that are used to irradiate a material and estimate the weight of the fat content and the entire weight.